Parathyroid Hormone Effects on Amino Acid Transport Into Bone Cells

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Abstract
The effect of parathyroid hormone on the transport of the model amino acid a amino isobutyric acid (AIB) has been studied in bone cells isolated mechanically from the metaphyses of 40-day-old rats. Chronic treatment with parathyroid extract (0.3 IU PTE/g body weight sc over 5 days) produced a 54% inhibition of AIB transport. The sequence of events after a single large dose of PTE (1 IU/g body weight sc) was subsequently investigated. In the first phase (8-12 hr after hormone administration) PTE stimulated AIB uptake (+30%), while in the second phase (48-72 hr.) the transport activity was decreased ([long dash]45%). A similar response to hormone occurred both in hypophysectomized and thyroparathyroidectomized animals, suggesting a primary effect of parathyroid extract rather than a compensatory reaction of thyroid or pituitary. These changes mirror changes in the biosynthesis of collagen previously observed in response to this hormone.